<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <script src="jquery-3.1.0.min.js"></script>
    <script src="selector.js"></script>
</head>
<body>
    <p>p1</p>
    <p id="pid">p2</p>
    <button>按钮</button>
</body>
</html>